From: Masami Hiramatsu <mhiramat@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: perf probe issues
Date: Wed, 15 Jun 2016 11:02:01 +0900 [thread overview]
Message-ID: <20160615110201.c2838ec2291cd9caaaa93ce4@kernel.org> (raw)
In-Reply-To: <20160614170504.GD3978@kernel.org>
On Tue, 14 Jun 2016 14:05:04 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> Hi Masami,
>
> While investigating a problem in the annotation code reported by
> Linus, with "kaslr" on the kernel command line and this in .config:
>
> [root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config
> CONFIG_RANDOMIZE_BASE=y
> # CONFIG_DEBUG_INFO is not set
> [root@jouet ~]#
>
> [root@jouet ~]# grep -w vfs_write /proc/kallsyms
> ffffffffac2404c0 T vfs_write
> [root@jouet ~]# perf probe vfs_write
> vfs_write is out of .text, skip it.
> Error: Failed to add events.
> [root@jouet ~]# perf probe -v vfs_write
> probe-definition(0): vfs_write
> symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (8 entries long)
> Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols
> Could not open debuginfo. Try to use symbols.
> vfs_write is out of .text, skip it.
> Error: Failed to add events. Reason: No such file or directory (Code: -2)
> [root@jouet ~]#
>
> Can you try to test with this config to investigate this problem?
Yes, I guess it missed to get start_text because of KASLR...
>
> We need to improve the error messages, for instance:
>
> "Could not open debuginfo. Try to use symbols."
>
> I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it
> doesn't manage to find a vmlinux file, it will try to use kallsyms as a
> fallback, is that what is happening here?
Let me check that the perf symbol/map object uses kallsyms for kernel.
Anyway, if the target is not the kernel, do we change the message
as "trying to use symbols"?
>
> - Arnaldo
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2016-06-15 2:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 17:05 perf probe issues Arnaldo Carvalho de Melo
2016-06-15 2:02 ` Masami Hiramatsu [this message]
2016-06-15 17:43 ` Arnaldo Carvalho de Melo
2016-06-15 21:33 ` Masami Hiramatsu
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